Two different parts stop the trailer. The controller in the truck applies the trailer brakes while the trailer is plugged in. The breakaway switch applies them if the trailer separates, using the battery on the trailer. One does not do the other's job.
What the breakaway switch is for
Curt's breakaway-kit installation manual says the battery in the kit applies the trailer brakes when the pin is pulled, and that the kit is for one-axle or two-axle trailers with electric brakes. Curt says the trailer will not be held indefinitely, and not to use the kit as a parking brake. Curt also says kits are generally required at a gross trailer weight of 3,000 lbs or more, and to check local law. That sentence is Curt's. It is not a list of state statutes.
Tekonsha's brake-control instructions say to disconnect the trailer plug from the tow vehicle before testing a breakaway switch, or you may destroy the brake control. The same sheet says reversing the connection to a breakaway battery on the trailer will destroy the control.
Ford's 2025 RV and trailer towing guide says the tow vehicle's brakes are rated for the GVWR, not the GCWR, and that a separate functional brake system should be used for a trailer weighing more than 1,500 lbs when loaded. Ford also says many states require a separate system above that loaded weight. Ford does not name those states in that sentence. Do not treat 1,500 lbs as California's number. California's statute is below, and it uses different weights.
The rules that are actually on the books
49 CFR 393.43(d) says every trailer required to have brakes must have brakes that apply automatically and immediately on breakaway from the towing vehicle. Except for a trailer with three or more axles, every brake the trailer is required to have must apply. The brakes must stay applied for at least 15 minutes.
49 CFR 393.42 is the commercial rule for which wheels need brakes. A semitrailer at or under 3,000 lbs gross weight, if it is subject to that part, is not required to have brakes when its axle weight does not exceed 40 percent of the towing vehicle's axle weights. Heavier trailers subject to the part do not get that exception.
Those sections sit in the Federal Motor Carrier Safety Regulations. 49 CFR 390.3 says the rules in that subchapter apply to employers, employees, and commercial motor vehicles that transport property or passengers in interstate commerce. 49 CFR 390.5 defines that vehicle to include one used on a highway in interstate commerce to transport property when the GVWR, GCWR, gross vehicle weight, or gross combination weight is 10,001 lbs or more. A private trip to a campground is not, by itself, interstate commerce. If you are being paid to haul, read the rule. If you are not, it is the wrong rule to quote as your duty.
California is a real state rule, and it is one state. Vehicle Code 26304(a) says power brakes on a trailer or semitrailer manufactured after December 31, 1955, operated on a public highway, and required to have brakes, shall be designed to apply automatically on breakaway and shall be capable of stopping and holding that vehicle stationary for not less than 15 minutes. Other states write their own equipment rules. This page does not recite a state it has not read.
How Curt says to test the kit
Curt's manual says not to run the test with the trailer's 7-way connected to a tow vehicle. It says to lift the trailer on a jack and jack stands so a wheel can spin clear of the ground, spin a wheel, and pull the pin. The wheel should stop. Curt says to leave the pin out for 15 minutes and confirm the wheel still will not spin, then put the pin back and lower the trailer. Curt says the battery needs a recharge after that test. The built-in charger, in that manual, charges when the 7-way is connected to a running vehicle.
Tekonsha's brake-adjustment notes, in the same brake-control sheet, say never to crawl under the trailer unless it is on properly placed jack stands, and not to lift or support the trailer on any part of the axle or the suspension. Follow the trailer maker's lifting instructions. A fifth wheel is a poor place to improvise a jack point.
After the test, the pin goes back in before you move the trailer. A pin left out is the switch doing the thing it does in a separation.
Setting the controller
Ford says an electronically controlled trailer brake usually has a control within reach of the driver and can be applied manually or automatically. It also says many electric-over-hydraulic systems are compatible with Ford's factory trailer brake controller. Tekonsha sheet N90160 says that particular control is not designed for electric-hydraulic systems. Read the sheet for the box in your truck before you follow anyone else's steps.
For the Tekonsha control in N90160, for 2, 4, and 6 brake applications, the printed setup is:
- Connect the trailer.
- With the engine running, hold the manual control full left and set the power knob to about 6.0.
- On a dry, level, paved surface, at 25 mph, fully apply the manual knob.
- If the trailer wheels lock, turn the power down. If the braking is not enough, turn it up.
- Repeat until the power is just below wheel lock, or at a force that gives the maximum braking the sheet describes.
- Then make a few low-speed stops with the brake pedal. That sheet says trailer braking starts and stops with the stoplight switch.
That 6.0 is a starting point in that sheet, not a rating and not a setting for a Ford factory controller or for an electric-over-hydraulic actuator. If the trailer brakes are electric-over-hydraulic, use the actuator maker's instructions and the truck maker's instructions.
The towing check compares weights. It does not check that the breakaway battery is charged or that the gain matches this trailer. The door-sticker guide is where GVWR and GCWR are defined, which is the distinction Ford uses for the truck's own brakes.
Test the breakaway with the trailer unplugged, then plug it back in only after the pin is seated. A controller that was cooked by a plugged-in test cannot apply the brakes on the next hill.
Questions people ask
- Does the FMCSA breakaway rule apply to a private camping trip?
- 49 CFR 390.3 applies Part 393 to commercial motor vehicles transporting property or passengers in interstate commerce. A private trip is not that rule by itself. California has its own equipment statute.
- Why unplug the trailer before a breakaway test?
- Tekonsha's brake-control instructions say to disconnect the trailer plug first, or the test may destroy the control. Curt says not to run its kit test with the 7-way connected.
- Is there one gain number for every controller?
- No. The 25 mph procedure below is the one printed in Tekonsha installation sheet N90160. A different controller, including a factory controller, has its own instructions.